AWS what? There's a lot more than one AWS code. If you're referring to D1.1, it does not have provisions for grouping materials that are unlisted in Table 3.1 or Annex M. Table 4.7 covers the limitations of base metal group combinations permitted by PQR testing.
Get a copy of AWS B2.1 -2009 Specification for Welding Procedure and Performance
Qualification. This specification provides material group numbers and list of base materials.
Just be aware that invoking B2.1, and the associated material groupings therein, needs to be accepted for use by "The Engineer". Not a big deal for most, but can be an area of heartburn if you have a less-than-understanding client doing the design and you're the fabricator.
As Mr168 points out, most clients consider themselves 'The Engineer' and will not accept the clause in the code, probably due to ignorance. But worth checking first to get your ducks in a row for a substantiated debate, which probably will not go your way. Good luck!
